I think you're on the right track. Madreferee helped me get mine sorted out. He's one of our leading experts.
On my FEL, the power beyond port is built in to the FEL valve assembly. I've tapped into the FEL PB port and have it feeding my backhoe hydraulics gang valve assembly, the return from the back hoe valve goes directly into my transmission (HYDRO). My 3 point hitch is the last one in the circuit normally but is integral to the tranny, so, when I attach the Backhoe, the 3 point hitch doesn't operate because the hoe then becomes the last one in the circuit dumping directly int the Hydro trannsimission.
When I take the backhoe off, I reconnect the jumper hose and that places the 3 point as the last valve in the circuit and it works out just fine.
If I wanted to add another Valve assembly, say for a grapple, I'd have to place it between the FEL valve and the backhoe jumper hose that feeds the backhoe valve, so when I removed the hoe, both the FEL valve and the new AUX valve would work independently with either the hoe or the 3 point hitch working. The returns can be Teed together for the FEL and AUX valves.
Shouldn't have to port around anything on the FEL. The new valve with PB ports should have its own built in relief and port and can be set right to match the system.